Spectroscopy of Hi : planets , chaos and the Universe

This review discusses the molecular ion and its deuterated isotopomers. The ion is important because of its fundamental nature, astrophysical significance and dynamical richness. The following topics are discussed: the discovery of H l , its unusual bonding and the important role played by ab initio electronic-structure calculations; the formation of H: and its importance in models of the interstellar medium; the unusual spectroscopy of H: and the accurate quantum calculations which led to laboratory observations; the failure to detect H: in the interstellar medium and its accidental observation in Jupiter; work on H: in the giant planets and other astronomical emission spectra: the very unusual infrared photodissociation spectrum of H: ; and the classical and quantal behaviour of the molecule at its dissociation limit. This review was received in December 1994. 0034-4885/95/040421+56$59.50